(i) Field of the Invention
This invention relates to a method of printing textiles and other materials using a transfer sheet or web which carries a pre-printed pattern or design.
(ii) Prior Art
Strenuous efforts have been made for many years to develop a transfer printing system for decoration of textiles since a satisfactory system of this kind has many advantages. One obvious advantage to the textile manufacturer is that he does not need to invest in expensive printing equipment or to employ the necessary skilled printing operatives. Almost as important an advantage is that it enables the textile manufacturer to hold stock in unprinted fabric and transfer webs, which involves a much reduced investment in stock and greater flexibility.
Despite these advantages, only one type of transfer printing system has become widely used for textile decoration and that is the vapor phase transfer system. In vapor phase transfer systems, a design is printed on a carrier web using an ink containing dyestuffs which sublime at temperatures of about 180.degree. to 250.degree. C. The carrier web is placed in contact with the fabric to be decorated and the design transferred by heating the carrier web, which is usually paper, to a temperature at which much of the dyestuffs in the design sublime and recondense onto the fabric. A typical vapor transfer method of this kind is described in British Pat. No. 1,433,763 (Sublistatic S.A.) Fabric dyed by vapor phase transfer has good "handle" and in the case of polyester fiber the process results in reasonably fast dyeing. The main limitations of vapor phase, dyeing, however, are that it is not suitable for dyeing cellulosic fibers such as cotton, since sublimable dyes are not fast towards such fibers, and also the process is rather slow, requiring a residence time of up to 30 seconds to complete dye transfer.
German Patent Application Ser. No. 2,505,940 (Lewis and Rattee) describes a process for applying a decoration to a textile from a transfer web in which a thermoplastic film incorporating the decoration is transferred bodily from a carrier web and adhered to the textile system, the thermoplastic film is formulated as a thermoplastic adhesive so that under the influence of heat it becomes soft and tacky. By selecting a carrier sheet having a release surface (e.g. a siliconized paper) the hot, tacky film, incorporating the design, can be made to adhere to the textile and, on subsequent cooling, the film can be stripped from the carrier, leaving the film bonded to the surface of the textile. Several problems soon become apparent when attempting to carry out the Lewis and Rattee process in practice. A fundamental problem is that the dyes or pigments forming the design in the transferred film have to be conveyed from the film into the fibers of the fabric and the polymer matrix forming the film removed or dispersed since otherwise the fabric has the appearance and handle of a plastic coated material. A satisfactory solution to this problem is not apparent from the German application since subsequent heating of the fabric bearing the transferred film in contact with metal plates or rollers would be likely to result in contamination of the plates and rollers with the tacky mass produced by heating the film. A further difficulty arising from the Lewis and Rattee system is that high quality printing onto surfaces having release characteristics is not possible since the poor wettability of such surfaces results in repellency and other printing defects. Finally, the need to cool the film prior to stripping introduces an undesirable limitation on the maximum possible speed of the process.
Attempts have also been made to produce a transfer system in which a liquid printing ink is reconstituted at the instance of application to the textile fabric. Theoretically such a system would be expected to be the most satisfactory approach since it would seem to reproduce most closely conventional printing from inked plates or rollers. In practice, successful realization of a system of liquid phase transfer has been thwarted by the problem of formulating an ink which would melt to a printable liquid at a temperature low enough not to damage the fabric and at the same time be solid and non-tacky at room temperature so that the transfer web or sheets can be stacked or reeled without blocking or marking off. Prior systems of this kind therefore are essentially compromises in that some blocking of the transfer sheets has to be tolerated and relatively high temperatures and transfer pressures adopted to ensure transfer of the design to the fabric. Severe conditions of operating temperatures and pressures are undesirable since they may distort or damage the fabric. Prior systems of this latter type are described in U.S. Pat. Nos. 2,583,286 (Albini-Colombo) and 2,911,280 (Cicogna).